In downhole exploration and production systems, a transmission line is often used in drill pipes and with downhole tools to convey data and instructions downhole or uphole. Sections of pipes that are coupled together to extend the downhole reach of the equipment are often configured as mating pin and box pairs that thread together. Because the threads on both the pin and box sides must sometimes be re-machined, the unthreaded portion at the tip of the pin as well as at the box thread runout follow geometric rules and limitations with regard to radial design space.